uninstall.php

<?php
/**
 * Fired when the plugin is uninstalled.
 *
 * @package   Recently
 * @author    Hector Cabrera <me@cabrerahector.com>
 * @license   GPL-2.0+
 * @link      http://cabrerahector.com
 * @copyright 2022 Hector Cabrera
 */

// If uninstall, not called from WordPress, then exit
if ( ! defined( 'WP_UNINSTALL_PLUGIN' ) ) {
	exit;
}

// Run uninstall for each blog in the network
if ( function_exists( 'is_multisite' ) && is_multisite() ) {

	global $wpdb;

	$original_blog_id = get_current_blog_id();
	$blogs_ids = $wpdb->get_col( "SELECT blog_id FROM {$wpdb->blogs}" );

	foreach( $blogs_ids as $blog_id ) {

		switch_to_blog( $blog_id );

		// Delete plugin's options
		delete_site_option( 'recently_ver' );
		delete_site_option( 'recently_config' );
		delete_site_option( 'recently_rand' );
		delete_site_option( 'recently_transients' );

		// delete thumbnails cache and its directory
		recently_delete_thumb_cache();

	}

	// Switch back to current blog
	switch_to_blog( $original_blog_id );

} else {

	// Delete plugin's options
	delete_option( 'recently_ver' );
	delete_option( 'recently_config' );
	delete_option( 'recently_rand' );
	delete_option( 'recently_transients' );

	// delete thumbnails cache and its directory
	recently_delete_thumb_cache();

}

function recently_delete_thumb_cache() {
	$wp_upload_dir = wp_upload_dir();

	if ( is_dir( $wp_upload_dir['basedir'] . "/recently" ) ) {
		$files = glob( $wp_upload_dir['basedir'] . "/recently/*" ); // get all file names

		if ( is_array($files) && ! empty($files) ) {
			foreach($files as $file){ // iterate files
				if ( is_file($file) )
					@unlink($file); // delete file
			}
		}

		// Finally, delete recently's upload directory
		@rmdir( $wp_upload_dir['basedir'] . "/recently" );

	}
}